The present invention relates generally to a key-activated security device and more specifically, to a method and apparatus to program the security device to recognize a spare key for an automotive vehicle.
Several security systems are available where a conventional key is combined with coded electronic circuitry to provide added security by increasing the total number possibilities able to satisfy the security device. However, the systems fail to disclose a convenient method for an end user to program a spare key into such a system.
For instance, U.S. Pat. No. 4,990,906 describes a microprocessor controlled programmable vehicle anti-theft device, where the system memory is cleared during a new key programming sequence. The security code of the new key is then placed into the memory. The new key security code is the only security code retained, thus any previously programmed keys become invalid. Also in order to program the new key into the system, the inputs of the microprocessor must be varied in a fixed sequence which requires trained service personnel.
It would be desirable to have a security system which could easily be programmed by an end user and which could store several key code values rather than one key code value in memory.